1. Field of the Invention
The present invention relates to pulleys in a continuously variable transmission applied mainly to vehicles such as an automobile, a motorcycle or the like.
2. Description of the Prior Art
In general, a continuously variable transmission is composed of a pair of opposite half pulleys with inner surface in taper form, and one or both half pulleys are made movable in the axial direction thereby distance between both half pulleys can be adjusted, and a belt hung to the pulley is moved upward or downward by wedge effect due to taper form of the inner surface of the half pulleys when the distance between both half pulleys is varied so that effective radius of the pulley is adjusted and the rotating speed ratio to other pulley connected to the pulley through the belt is adjusted continuously.
In the prior art, in such speed change mechanism, the half pulleys are moved in the axial direction by means of oil pressure or centrifugal force.
However, according to oil pressure, hydraulic control mechanism such as a hydraulic pump, a pressure adjusting valve or the like is required thereby the structure is complicated and expensive, and working failure may occur due to oil leakage. Also according to centrifugal force, fine adjustment of centrifugal force is very difficult and moreover generation of constant centrifugal force is also very difficult thereby the working becomes rough and unstable.
In a transmission in the prior art, when motion to narrow the distance between both half pulleys is performed at the main drive side, since the speed change is performed at the state that effective tension always acts on an endless belt, problem occurs in that the power transmission efficiency is deteriorated or breakage of the endless belt becomes hard. That is, force required for transmission of the endless belt becomes sum of belt thrust in an input pulley and an output pulley (thrust force in the axial direction for clamping so that the endless belt and the input and output pulleys do not slip), and force of pushing-out the endless belt at the output side towards the outside and force of pushing-in the endless belt at the input side towards the inside, thereby considerable transmission loss is produced.
Further in a continuously variable transmission in the prior art, if an endless belt of narrow V-angle having high friction coefficient is used, excessive tension acts on the endless belt at sudden transmission thereby problem occurs in that the endless belt is pushed to the input and output pulleys and may bite them.
A continuously variable transmission is provided with a mechanism of transmitting the rotating force to both the outer rotary shaft and the inner rotary shaft being mutually slidable.
Such rotating force transmitting mechanism in the prior art, as shown in FIG. 7, comprises a cylindrical outer rotary shaft 61 and an inner rotary shaft 62 which is inserted in the outer rotary shaft 61 in relatively slidable state. The outer rotary shaft 61 is provided with a key way 63 in the axial direction and the inner rotary shaft 62 is provided with a key 64, and the key 64 is fitted to the key way 63. For example, when the inner rotary shaft 62 is made a driving shaft and the outer rotary shaft 61 is made a driven shaft, the rotating force of the inner rotary shaft 62 is transmitted through the key 64 and the key way 63 to the outer rotary shaft 61.
The above-mentioned constitution in the prior art is disadvantageous in that relative slide resistance between the outer rotary shaft 61 and the inner rotary shaft 62 becomes large due to friction produced between the key 64 and the key way 63.